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Abstract
Seasonal data for one year on the flora and fauna associated with Cladophora albida (Huds.) Kütz from four rockpools (3 high-shore, 1 mid-shore) on Great Cumbrae Island, Firth of Clyde, Scotland are presented. A total of 131 858 animals was censussed. The mid-shore pool had a significantly lower annual mean density than the high-shore pools. Only at the most exposed site was a distinct seasonal trend apparent (lowest faunal density in spring, highest in summer). Species number showed no marked seasonal fluctuations neither did equitability. The lowest diversity was found in the mid-shore pool. Epiphytic cyanobacteria were present throughout the year. Diatoms were absent in the summer; possibly because of intense grazing by meiofaunal herbivores. The reduction in overall faunal density in the mid-shore pool was caused by the absence of large numbers of nematodes at this site related to the reduced availability of detritus and sand grains, perhaps reflecting greater wave scouring at this level on the shore. Large meiofaunal populations overwinter successfully in Cladophora in these ice-free latitudes and sheltered waters. Nematodes and harpacticoid copepods dominate the fauna of Cladophora in these permanent pools. Even populations in high-shore situations are remarkably stable. The rhombognathid mites, the polychaetes Fabricia sabella and Janua pagenstecheri and the chironomid larvae all showed little or no seasonal fluctuations in numbers, though most harpacticoid copepods, ostracods, turbellarians and archiannelids had very definite population maxima. Cladophora also acts as a nursery ground for species whose adults live elsewhere on rocky shores.